1. Field of the Invention
The present invention relates, in general, to an injection nozzle of an injection molding machine used for injecting pressurized and melted resin into the cavity of a mold and, more particularly, to an injection nozzle having a nozzle tip at its lower end and provided with a cushion ring at a position between a nozzle body and the nozzle tip, said cushion ring not only relieving pressure acting on the nozzle tip when the nozzle thermally expands by a heater during an injection of melted resin into the cavity of a mold and thereby preventing the core of the cavity from breakage, but also biasing the nozzle tip onto the core, thus preventing the melted resin from leakage during an injection molding process.
2. Description of the Prior Art
As well known to those skilled in the art, when forming a synthetic resin product through an injection molding process, melted resin under high pressure is injected from an injection cylinder into the cavity of a mold through the injection nozzle of a manifold. In order to allow the lower end of the injection nozzle to be smoothly inserted into the core of the cavity of the mold prior to injecting the melted resin into said cavity, an insert hole, having a diameter larger than the outer diameter of the lower end of the injection nozzle, is formed on the core of the cavity. Such an insert hole forms a gap at a position around the lower end of the injection nozzle. When the melted resin is injected into the cavity, the resin is introduced into the gap around the lower end of the nozzle. The resin in the gap is continuously heated by the heater, provided around the injection nozzle, resulting in that said resin may be plastically deformed, discolored or changed in its physical characteristics. Said resin is, thereafter, introduced into the cavity, thus deteriorating the quality of the product. Such a problem is prominent particularly when producing white products through an injection molding process. It is thus necessary to overcome such a problem. When a product, having different colors, is produced through an injection molding process, the resin, introduced from the gap into the cavity, is mixed with the resin directly injected from the nozzle into the cavity, thus reducing the quality of the products. In an effort to overcome the above problems, the injection nozzle is positioned relative to the cavity of a mold in a way such that the lower end of the nozzle is brought into pressure contact with the core of the cavity, thus preventing leakage of the resin from the junction between the nozzle and the core. However, the injection nozzle is heated by the heater and thermally expands, thus biasing the core of the cavity and causing a crack in the core. In such a case, the mold has to be changed with a new one and this forces the user to pay money for the molds and increases production cost of the injection molded products.